Sea level changing all the time, NZ scientists discover

By PAULA OLIVER

A decade ago Derek Goring was frustrated by a lack of information about New Zealand's sea levels - so he set about fixing the problem.

Along the way the Niwa scientist and his colleague Rob Bell have helped out brides and grooms, carnival organisers and the Ministry of Civil Defence and Emergency Management.

Through a network of recorders around the country's coastline, the pair are finding out how remarkably variable our sea levels are, even between geographically close points.

At Kaiteriteri, at the top of the South Island, sea levels can change 5m with the tide, but at nearby Kapiti Island the range is only 2m. And on the Piha side of Auckland the sea fluctuates more than it does in the Hauraki Gulf.

"When I present this to Americans they typically say 'wow, fancy having all that happening in such a small area'," Dr Goring says. "It's genuinely remarkable."

It happens because New Zealand is a very small land mass sitting in the middle of huge oceans, on which it has very little influence.

Since 1992 Dr Goring and his colleagues have installed almost 20 recorders around the coast, including one on the Chatham Islands and another at Scott Base in Antarctica.

The data the $50,000 stations provide is valuable for all kinds of people.

Niwa has fielded calls from brides and grooms trying to plan beach weddings, who are concerned about what will happen with tides in 18 months.

Local authorities use the data to help plan the building of coastal structures such as outfalls.

But one of the most striking uses has been in monitoring tsunamis.

In 2001 an earthquake measuring eight on the Richter Scale struck Peru - 16 1/2 hours later recorders on the east coast of the South Island picked up the subsequent tsunami. More importantly, a recorder on the Chatham Islands picked it up 2 1/2 hours earlier.

The Chatham Islands recorder has since been upgraded with the help of Civil Defence, because it provides a warning of impending disaster.

"We know a tsunami is coming, but we never know how big it is until it gets to the Chathams. It can say it's a fizzer, or it's a big one. And if it's big, we better do something about it."

Further reading: nzherald.co.nz/marine